Method for the rapid setting of baryta coatings



METHOD FOR THE RAPID SETTING F BARYTA COATINGS Thomas G. Hanley, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application March 31, 1954,

Serial No. 420,209

Claims. (Cl. 117-60) This invention relates to a method of applying baryta coatings to paper characterized by applying a buffer material to the paper and applying the baryta coating thereover.-

in the preparation of baryta coated paper for use for photographic purposes there is a tendency for the baryta coating to exhibit surface roughness. This appears to be due to the fact that the coating as applied to the paper is in the fluid or mobile state and as the sheet is dried, such as in a festoon drying system, gravitational flow occurs causing unevenness of the surface of the coating. There have been suggestions of the rapid setting of baryta coatings by fuming operations but sometimes surface roughness characteristics are not overcome by that treatment of the baryta coatings.

One object of my invention is to provide a method for the rapid setting of the coating in a baryta coating operation. Another object of my invention is to provide a setting method for baryta coatings which take eflect before surface roughness occurs and while the baryta coating is still in a smooth condition. Other objects of my invention will appear herein.

.1 have found that baryta coatings free of surface roughness may be obtained by incorporating into paper at least upon the surface thereof a butfer material which will cause the rapid setting of baryta coatings thereon which have a substantial proportion of formaldehyde therein which coatings retain'their physical form, have good surface smoothness and may be readily dried.

In its broadest aspects my invention comprises a method of preparing a baryta coated paper in which the paper is first supplied with a photographically inert buffering material having a pH'value within the range of approximately 7-8 in which there is applied to the paper having the buffering material, at least on the surface thereof, a baryta coating composition, to that surface, which essentially consists of a white pigment such as barium sulfate or titanium oxide, gelatin as the binder therefor and a substantial proportionof formaldehyde therein. When the baryta composition comes in contact with the buffer-containing paper almost immediate setting of the baryta coating occurs in a form in which a smooth surface is obtained. This baryta coating is readily dried by means of a current of warm dry air, by any of the conventional methods for drying coatings of this nature and a paper is obtained having a baryta coating substantially free of the surface roughness which has characterized many baryta coatings previously. The baryta coated paper is then ready to receive a photographic emulsion layer such as of gelatin-silver halide emulsion thereover. 4i

United States Patent" O For the employment of my invention it is desirable that the liquid coating composition contain at least 2% of gelatin or other protein to assure the coating setting up in the desired form, although with some types of paper which absorb moisture even moredilute protein solutions may be set in accordance with the method which I have described. Any percentage of formaldehyde within the range of %50% (based on the weight of the protein) may be employed in the baryta coating composition although as a rule the most useful proportion of formaldehyde will be found within the range of /z10%. With an increase in the concentration of protein in the coating composition, the proportion of formaldehyde necessary to obtain rapid setting of the baryta coating may be reduced.

The amount of buffer which is supplied to the paper will vary depending upon whether the buffer is incorporated in the stock from which the paper is made or whether the buffer is applied as a coating on the surface of the paper. The amount of buffer needed on the surface of the paper is small. For instance, as long as the paper surface contains at least approximately 0.02 gram of buffer per square meter of paper surface, it is effective to cause a rapid setting of the baryta coating which is applied thereto.

The buffering material which is employed is any photographically inert buffer having a pH value approx imately within the range of 7.0-8.0. Buffers which have been found to be useful in the baryta coating of paper in accordance with our invention are the following: 1) citric acid-sodium phosphate, (2) sodium hydroxide-mono-potassium phosphate, (3) mono-potassium Example 1 A buffer solution having a pH value of 7.5 was prepared by dissolving 96 grams of citric acid and 2120 grams of trisodium phosphate in 20 gallons of water. This solution was applied to the surface of a sheet of high alpha-cellulose paper suitable for photographic purposes by means of coating equipment using a dip coating roll. The treated paper is dried and was found to have upon the surface thereover .8 gm. of trisodium phosphate and 0.4 gm. of citric acid per sq. meter of paper surface. If desired, this baryta coating may be applied to the paper while on the machine in its manufacture.

A baryta composition comprising 1 part of gelatin is dissolved in 5 parts of water and 10 parts of barium sulfate in the form of a 60% solid suspension in Water was added thereto. The mass was diluted to a total solids content of about 35% and there was added there to 0.67 part of iso-amyl alcohol (anti-foaming agent) and .35 part of a 40% aqueous formaldehyde solution. The composition was dispersed mechanically in a colloid mill and was applied to the surface of the paper containing the buffering agent by means of a dip coating roll. The baryta coating set almost immediatelyv and was dried. The paper thus formed was employed as a support for a gelatino-silver halide photographic emulsion.

Example 2 Paper was prepared in accordance with the procedure described in Example 1 except that the buffer solution employed comprised 58 grams of sodium hydroxide and 290 grams of monopotassium phosphate in 10 gallons of water which solution had a pH value of 7.4. The baryta coated paper had a coverage of .004 gram of sodium hydroxide and .02 gram of monopotassium phosphate per sq. meter of surface.

There was applied to the buffered surface of the dry paper a pigmented composition comprising 1 part of gelatin and parts of hot water with which had been mixed 12 /2 parts of barium sulfate in the form of a 60% solids with water. The mixture was diluted to a solids content of about 35% and formaldehyde and antifoaming agent were added in the proportion indicated in the preceding example. The composition was dispersed mechanically in a colloid mill and the dispersion was applied to the paper over the coating thereon to give a smooth surface which after drying was suitable for the application of a photographic emulsion thereto. Upon application of the pigmented composition to the paper almost immediate setting occurred.

Example 3 A buffer solution having a pH value of 7.0 composed of 140 grams of monopotassium phosphate and 270 grams of Nazi-IP04. 2H2O in gallons of water was coated onto photographic grade paper base and the resulting coverage of the buffer thereon was .007 gram of monopotassium phosphate and .014 gram of disodium phosphate per sq. meter of paper surface. A composition was prepared of 1 part of gelatin and 5 parts of hot water to which had been added 14 parts of dry water dispersible titanium dioxide, 0.35 part of a 40% aqueous formaldehyde solution and .67 part of n-butyl alcohol (anti-foaming agent). The composition was diluted with water to a solids content and was applied to the paper on the surface containing the buffering agent. Almost immediate setting of the pigment coating was obtained and the paper after drying was ready for the application of a photographic emulsion layer thereover.

Example 4 A baryta coating was applied to the surface of the baryta coated paper of Example 1 on the first baryta coating, the baryta composition used containing a small proportion of formaldehyde therein. It was found that the second baryta coating set almost immediately indicating that the buffering action of the paper Was effective on a second baryta layer applied over that first applied. The paper thus obtained after drying was ready for the application of a photographic emulsion layer thereover.

If the paper is such that a pigmented coating is to be applied to both sides of the paper, it is more convenient to incorporate the buffering material into the paper stock so as to give the desired bulfer effect on each side of the paper. However, both sides of the paper to be baryta coated may be coated first with butter solution prior to the application of the baryta thereto.

1 claim:

1. A method of preparing a baryta coated paper base having good surface characteristics which comprises supplying to at least one surface of the paper at least 0.2 gm. per sq. meter of a photographically inert buffering material having a pH value within the range of approximately 78 and applying to a surface of the paper so supplied a layer of a coating composition comprising a pigment, a protein and A-50% (based on the weight of the protein) of formaldehyde.

2. A method of preparing a baryta coated paper base having good surface characteristics which comprises supplying to at least one surface of the paper at least 0.2 gram per sq. meter of a photographically inert buffering material having a pH value within the range of approximately 7-8 and applying to a surface of the paper so supplied a layer of a coating composition comprising a pigment, gelatin and A50% (based on the weight of the gelatin) of formaldehyde.

3. A method of preparing a baryta coated paper base having good surface characteristics which comprises applying to at least one of the surfaces of the paper, at least 0.2 gram per sq. meter of a photographically inert buffering material having a pH value within the range of approximately 7-8 and applying to the surface of the paper so supplied a layer of a coating composition comprising a pigment, gelatin and /1-50% (based on the weight of the protein) of formaldehyde.

4. A method of preparing a baryta coated paper base having good surface characteristics which comprises applying to at least one surface of the paper of at least 0.2 gram per sq. meter of a photographically inert buffering material having a pH value within the range of approximately 7-8 and applying to the surface of the paper so supplied a layer of a coating composition comprising a pigment selected from the group consisting of barium sulfate and titanium dioxide, a protein and A- 50% (based on the Weight of the protein) of formaldehyde.

5. A method of preparing a baryta coated paper base having good surface characteristics which comprises supplying to one surface of the paper at least 0.2 gram per sq. meter of a photographically inert buffering material having a pH value Within the range of approximately 7-8 and applying to a surface of the paper so supplied a layer of a coating composition comprising barium sulfate, gelatin and Mi -50% (based on the Weight of the gelatin) of formaldehyde.

6. A method of preparing a baryta coated paper base having good surface characteristics which comprises supplying to at least one surface of the paper at least 0.2 gram per sq. meter of a photographically inert buffering material having a pH value within the range of approximately 7-8 and applying to a surface of the paper so supplied a layer of a coating composition comprising titanium dioxide, gelatin and %-50% (based on the weight of the gelatin) of formaldehyde.

7. A method of preparing a baryta coated paper base having good surface characteristics which comprises supplying to at least one surface of the paper at least 0.2 gram per sq. meter of a buffering material having a pH value wtihin the range of approximately 78 selected from the group consisting of (l) citric acid-sodium phosphate (2) sodium hydroxide-monopotassium phosphate, (3) monopotassium phosphate-disodium phosphate, (4) acetic acid-sodium acetate and (5) ammonium acetatemonopotassium phosphate-borax and applying to a surface of the paper so supplied a layer of a coating composition comprising a pigment, a protein and %50% (based on the weight of the protein) of formaldehyde.

8. A method of preparing a baryta coated paper base having good surface characteristics which comprises supplying to at least one surface of the paper at least 0.2 gram per sq. meter of a buffering material having a pH value within the range of approximately 7-8 composed of citric acid and sodium phosphate and applying to a surface of the paper so supplied a layer of a coating composition comprising barium sulfate, gelatin and /z50% (based on the weight of the gelatin) of formaldehyde.

9. A method of preparing a baryta coated paper base having good surface characteristics which comprises supplying to at least one surface of the paper at least 0.2 gram per sq. meter of a buffering material having a pH value within therange of 7-8 comprising sodium hydroxide and monopotassium phosphate and applying to a surface of the paper so supplied a layer of a coating 5 composition comprising barium sulfate, gelatin and lb- 10% (based on the weight of the protein) of formaldehyde.

10. A method of preparing a baryta coated paper base having good surface characteristics which comprises sup- 5 plying to at least one surface of the paper at least 0.2 gram per sq. meter of a buffering material having a pH value within the range of approximately 7-8 comprising monopotassium phosphate and disodium phosphate and applying to a surface of the paper so supplied a layer 10 References Cited in the file of this patent UNITED STATES PATENTS Howard July 10, 1945 Jones Sept. 15, 1953 

1. A METHOD OF PREPARING A BARYTA COATED PAPER BASE HAVING GOOD SURFACE CHARACTERISTICS WHICH COMPRISES SUPPLYING TO AT LEAST ONE SURFACE OF THE PAPER AT LEAST 0.2 GM. PER SQ. METER OF A PHOTOGRAPHICALLY INERT BUFFERING MATERIAL HAVING A PH VALUE WITHIN THE RANGE OF APPROXIMATELY 7-8 AND APPLYING TO A SURFACE OF THE PAPER SO SUPPLIED A LAYER OF A COATING COMPOSITION COMPRISING A PIGMENT, A PROTEIN AND 1/4-50% (BASED ON THE WEIGHT OF THE PROTEIN) OF FORMALDEHYDE. 